While many fancy tails displayed by male birds serve solely to attract mates (SN: 2/6/93, p. 84), not all tails serve this purpose. To find out whether long tails evolve primarily as sex symbols or aids to survival, British biologists analyzed the aerodynamics of various tail shapes. In general, longer tails add more drag, but long tails with shallow forks can improve flight efficiency, Andrew Balmford, now at the Zoological Society of London, and two colleagues report in the Feb. 18 NATURE. For the study, they calculated the lift and drag of various tail models and measured the tail feathers in 600 preserved bird skins. Birds that spend much of their time flying often possess these efficient tails. In these species, the females also tend to evolve such tails, the researchers note.

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